Measures are conventionally taken in a wide range of weather conditions for ensuring that highways, major urban roads and even more minor routes are kept open for traffic. In cold countries, or during wintery periods in more temperate climates, salt, grit or other substances are dispensed onto road surfaces to ameliorate driving conditions, for example by preventing or reducing build up of ice. Hereinafter the salt, grit or other substances, whether or not particulate, will be referred to simply as "grit", while the process by which they are applied will be termed "gritting".
Gritting is conventionally performed by gritting vehicles which carry a store of grit and travel along a predetermined route distributing grit across the road surface as they travel. Grit is dispensed at a substantially constant rate, although in special circumstances the driver may increase the rate.
Producing and supplying large quantities of grit is expensive. Furthermore, besides the beneficial effects of gritting there are also important detrimental effects Some grits cause significant environmental damage, or are corrosive to vehicles. For these reasons it is desirable that the amount of grit dispensed is minimised, while ensuring that roads are effectively treated.
Development in the technology is slow, since gritting is a vital safety service and no modification can be tolerated if it may reduce effectiveness. Nevertheless, techniques have recently been devised to help determine more accurately when it is necessary to carry out gritting. One such technology makes a "thermal map" of a geographical area by surveying the area to determine a map of the local temperature variations, due e.g. to exposure to cold winds. In particular a relevant kind of thermal map indicates which parts of major roads are prone to low temperatures. This fixed information can be combined with periodically or continuously updated information from local weather stations concerning actual weather in specific locations, to produce a "forecast thermal map" which approximates a predicted actual temperature distribution in a region. Graphical information can then be generated showing estimated temperature variation along each of the predetermined potential gritting routes, and hence showing which of such routes include stretches of road which are liable to become icy. If the entire length of a route should be free from ice, no gritting vehicle need pass along it. If it is found that a given route includes a potentially icy stretch of road then a vehicle is sent.
DE-A-3938147 describes a gritting system which seeks to reduce the mentioned difficulties by pre-determining a gritting rate profile based on knowledge of the route's temperature variation characteristics and the prevailing weather conditions; the profile is loaded into an on-board computer and used to operate a control mechanism for the gritting apparatus, controlling spreading density, width and lateral distribution profile. Change from one mode of spreading to another is actuated by occasional reflector plates positioned adjacent the route, which reflect radiation beams back to the vehicle.
In its broadest terms, the present invention proposes a gritting system in which the position of at least one gritting vehicle (preferably plural gritting vehicles) is monitored, preferably at an external control or tracking station and preferably substantially continuously or regularly.
In a first aspect we provide a method of gritting in which the location of at least one gritting vehicle is monitored and the dispersement of grit is controlled in dependence on a predetermined gritting requirement at that location. In this way, the efficiency of the gritting may be enhanced.
The control is preferably exercised in dependence upon a predicted temperature at the location of the gritting vehicle, e.g. the predicted temperature of that location according to a forecast thermal map.
As a first example, grit may be dispensed only along portions of the route including stretches which the forecast thermal map has estimated to be at or below zero degrees Celsius. The gritted portions may in fact substantially correspond to the sub-zero stretches of the route, but, more preferably, they include also adjacent stretches of the road so as to produce a safety margin.
As a second example, the control may not merely determine whether or not grit is dispensed along a given stretch of road but, more preferably, additionally (or indeed alternatively) the rate at which grit is dispensed. Thus, grit may be applied at a greater rate to those regions which are predicted to be at a lower temperature. Such control of the rate at which grit is dispensed optionally depends also upon the velocity of the gritting vehicle, for example so that the density of grit application (ie. rate of release of grit/velocity of the gritting vehicle) obeys a predetermined relationship with the predicted temperature.
The control of grit dispersion may in either case be automated, i.e. control means may be provided which controls the rate of gritting automatically in dependence on the predetermined local gritting requirement. Or, control may be via a human operator. For example the mechanism may calculate automatically whether or not, or to what extent, gritting should occur, and transmit a corresponding instruction to the driver of the gritting vehicle (eg. by indication lights or voice synthesis). The driver then controls the rate of gritting accordingly. Preferably, even in the most automated embodiments, the operator is able to at least influence the gritting, albeit as a manual override of an automatic mechanism, to exploit his or her personal knowledge, for example a knowledge of small local frost hollows or the presence of water on the road due to a burst pipe.
Preferably, a gritting vehicle carries one or more sensors for measuring at least one local weather or surface condition, for example surface temperature or residual salinity. Control of gritting may then be carried out also in dependence on the results of the measurement. For example, it is possible to monitor in real time any discrepancy between the predicted temperature in the vicinity of the gritting vehicle and the actual temperature. This permits updating and/or correction of the forecast thermal map. Thus, feedback is possible in which the gritting is controlled in real time in dependence upon measurements derived by the gritting vehicle. Another possibility is that the gritting rate is controlled in substantial or full dependence on such real-time measurements from one or more on-board sensors. In such cases a forecast thermal map may be used only for e.g. route selection (see below) and/or as a back-up indicator of the amount of grit required.
The control of gritting need not only be a control of the rate of gritting, but may additionally or alternatively include a control of the route taken by a gritting vehicle. Accordingly, in a second aspect the invention provides a method of gritting in which the location of at least one gritting vehicle is monitored and the route of the at least one gritting vehicle is controlled in dependence on the measured location of the vehicle.
As a first example, the route of a gritting vehicle need not be predetermined but may be selected on the basis of a forecast thermal map, for example so as to cover efficiently all especially cold roads. In this case, the monitored position of the gritting vehicle can be used to generate directional instructions to the driver.
A second example is when, as described above, a comparison of the information derived from one or more weather sensors mounted on the vehicle with the data from the corresponding location on the forecast thermal map indicates that weather has deteriorated. In this case, an update of the forecast thermal map may demonstrate that additional grit should be applied to a given stretch of road. Accordingly the gritting system may assign a gritting vehicle to perform the additional gritting of the road. The assignment preferably takes into account the location of the gritting vehicles, and/or the amount of grit each is carrying.
In a third aspect, the invention may provide a method of gritting in which the location of at least one gritting vehicle is monitored and the location information is collected in real time off the gritting vehicle or vehicles, for example after transmission to a central database. Thus, reliable and secure archiving may be performed, for example to establish whether or not gritting was performed correctly.
A desirable feature of a gritting system would be an accurate recordal or "archiving" of the manner in which gritting is carried out. This record can be valuable in the event of an accident, in determining whether gritting was adequate and apportioning liability. Accurate and secure records are becoming increasingly important because of the legal duty of ensuring that gritting is done correctly. At present no system of archiving is more sophisticated than a simple measurement and recordal of the weight of a gritting vehicle at the beginning and the end of a gritting session, from which only the average rate of gritting can be recorded.
In each aspect the monitoring of location is preferably by a Global Positioning System (GPS), that is a system in which an object is located by reception at that object of data transmitted by a global satellite. The use of such equipment is well known for locating ships and other vehicles, but has not been associated with gritting. Conventional GPS has an accuracy of only about 50-100 m. To determine which road the gritting vehicle is on even in an urban environment, the present invention preferably uses a variety of GPS known as a "Differential Global Positioning System" (DGPS), which increases the accuracy of the position determination to within a few meters. DGPS reduces noise in the signal received from a satellite by comparing the signal received from an antenna mounted on the gritting vehicle with a corresponding signal received by one or more stationary receivers in known locations, so that the location of the gritting vehicle can be derived from the difference between the two sets of signals. DGPS is a known technology per se.